package com.icss.ah.base.util;

import java.io.ByteArrayOutputStream;

/**
 * Base64算法编码解码类
 * 
 * @author yanhao
 * @version 1.0
 */
public class Base64 {

	/** -----------------Base64编码表-------------------* */
	private static final char[] encodeTabel = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
			'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
			'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
			'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
			'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
			'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
			'w', 'x', 'y', 'z', '0', '1', '2', '3',
			'4', '5', '6', '7', '8', '9', '+', '/' };

	/** -----------------Base64解码表-------------------* */
	private static final byte[] decodeTabel = { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
			-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
			-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
			52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
			-1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
			15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
			-1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
			41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1 };

	/**
	 * 编码函数
	 * 
	 * @param bs
	 * @param offset
	 * @param length
	 * @return
	 */
//	public static byte[] encode(byte[] bs, int offset, int length) {
//		int blocks = (length / 3) + (length % 3 == 0 ? 0 : 1);
//		byte[] input = new byte[blocks * 3];
//		byte[] output = new byte[blocks * 4];
//		System.arraycopy(bs, offset, input, 0, length);
//		int inputOffset = 0;
//		int outputOffset = 0;
//		for (int i = 0; i < blocks; i++) {
//			encodeBlock(input, inputOffset, output, outputOffset, length);
//			inputOffset += 3;
//			outputOffset += 4;
//		}
//		return output;
//	}
	public static String encode(byte[] bs, int offset, int length) {
		StringBuffer sb = new StringBuffer();
		int a, b, c;
		while (offset < length) {
			a = bs[offset++] & 0xff;
			if (offset == length) {
				sb.append(encodeTabel[a >>> 2]);
				sb.append(encodeTabel[(a & 0x03) << 4]);
				sb.append("==");
				break;
			}

			b = bs[offset++] & 0xff;
			if (offset == length) {
				sb.append(encodeTabel[a >>> 2]);
				sb.append(encodeTabel[((a & 0x03) << 4) | ((b & 0xf0) >>> 4)]);
				sb.append(encodeTabel[(b & 0x0f) << 2]);
				sb.append("=");
				break;
			}

			c = bs[offset++] & 0xff;
			sb.append(encodeTabel[a >>> 2]);
			sb.append(encodeTabel[((a & 0x03) << 4) | ((b & 0xf0) >>> 4)]);
			sb.append(encodeTabel[((b & 0x0f) << 2) | ((c & 0xc0) >>> 6)]);
			sb.append(encodeTabel[c & 0x3f]);
		}

		return sb.toString();
	}

	/**
	 * 解码函数
	 * 
	 * @param bs
	 * @return
	 */
//	public static byte[] decode(byte[] bs) {
//		int count = 0;
//		int length = bs.length;
//		if (bs[length - 1] == '=') {
//			count++;
//			if (bs[length - 2] == '=') {
//				count++;
//			}
//		}
//
//		int blocks = length / 4;
//		length = blocks * 3;
//		byte[] input = new byte[length];
//		byte[] output = new byte[length -= count];
//		int inputOffset = 0;
//		int outputOffset = 0;
//		for (int i = 0; i < blocks; i++) {
//			decodeBlock(bs, inputOffset, input, outputOffset, length);
//			inputOffset += 4;
//			outputOffset += 3;
//		}
//		System.arraycopy(input, 0, output, 0, length);
//		return output;
//	}
	public static byte[] decode(String s) {
		byte[] bs = s.getBytes();
		int length = bs.length;
		ByteArrayOutputStream baos = new ByteArrayOutputStream(length);
		int offset = 0;
		int a, b, c, d;
		while (offset < length) {
			do {
				a = decodeTabel[bs[offset++]];
			} while (offset < length && a == -1);

			if (a == -1) {
				break;
			}

			do {
				b = decodeTabel[bs[offset++]];
			} while (offset < length && b == -1);

			if (b == -1) {
				break;
			}

			baos.write((a << 2) | ((b & 0x30) >>> 4));
			do {
				c = bs[offset++];
				if (c == 61) {
					return baos.toByteArray();
				}

				c = decodeTabel[c];
			} while (offset < length && c == -1);

			if (b == -1) {
				break;
			}

			baos.write(((b & 0x0f) << 4) | ((c & 0x3c) >>> 2));
			do {
				d = bs[offset++];
				if (d == 61) {
					return baos.toByteArray();
				}

				d = decodeTabel[d];
			} while (offset < length && d == -1);

			if (d == -1) {
				break;
			}

			baos.write(((c & 0x03) << 6) | d);
		}
		return baos.toByteArray();
	}
	/**
	 * 编码块
	 * 
	 * @param src
	 * @param srcOffset
	 * @param des
	 * @param desOffset
	 * @param length
	 */
//	private static void encodeBlock(byte[] src, int srcOffset, byte[] des, int desOffset, int length) {
//		int a = src[srcOffset++] & 0xff;
//		int b = src[srcOffset] & 0xff;
//		int c = src[srcOffset + 1] & 0xff;
//		des[desOffset++] = (byte) encodeTabel[a >>> 2];
//		des[desOffset++] = (byte) encodeTabel[(a << 4 & 0x30) | (b >>> 4)];
//		if (srcOffset >= length) {
//			des[desOffset++] = '=';
//			des[desOffset++] = '=';
//		} else {
//			des[desOffset++] = (byte) encodeTabel[(b << 2 & 0x3c) | (c >>> 6)];
//			if (srcOffset >= length - 1) {
//				des[desOffset++] = '=';
//			} else {
//				des[desOffset++] = (byte) encodeTabel[c & 0x3f];
//			}
//		}
//	}

	/**
	 * 解码块
	 * 
	 * @param src
	 * @param srcOffset
	 * @param des
	 * @param desOffset
	 * @param length
	 */
//	private static void decodeBlock(byte[] src, int srcOffset, byte[] des, int desOffset, int length) {
//		int a = decodeTabel[src[srcOffset++]];
//		int b = decodeTabel[src[srcOffset++]];
//		int c = decodeTabel[src[srcOffset]];
//		int d = decodeTabel[src[srcOffset + 1]];
//		des[desOffset++] = (byte) (((a << 2) & 0xfc) | (b >>> 4));
//		if (desOffset >= length) {
//			des[desOffset++] = 0;
//			des[desOffset++] = 0;
//		} else {
//			des[desOffset++] = (byte) (((b << 4) & 0xf0) | (c >>> 2));
//			if (desOffset >= length - 1) {
//				des[desOffset++] = 0;
//			} else {
//				des[desOffset++] = (byte) (((c << 6) & 0xc0) | d);
//			}
//		}
//	}
	public static void main(String[] args) {
		byte[] bs = "中华人民共和国".getBytes();
		String s = encode(bs, 0, bs.length);
		System.out.println(s);
		byte[] bs2 = decode(s);
		System.out.println(new String(bs2));
	}
}